1. Field of the Invention
The present invention relates in general to the photonics field and, in particular, to a lens array and a method for fabricating the lens array from a photosensitive glass plate that has a relatively small amount of a photosensitive agent (e.g., silver, gold or a combination thereof).
2. Description of Related Art
Today it is well known that a lens array can be made from a photosensitive glass plate. In fact, scientists at Corning Incorporated the, assignee of the present invention, have developed and patented a photosensitive glass plate known as FOTOFORM® glass and a process known as the SMILE® process which can be used to form a lens array. Detailed discussion relating to the SMILE® process is provided in U.S. Pat. Nos. 4,572,611, 4,518,222 and 5,062,877 the contents of which are incorporated herein by reference. While detailed discussion relating to FOTOFORM® glass is provided in U.S. Pat. Nos. 2,326,012, 2,422,472, 2,515,936, 2,515,938, 2,515,275, 2,515,942 and 2,515,943 the contents of which are incorporated herein by reference. An example of a traditional lens array that was fabricated from FOTOFORM® glass which was subjected to the SMILE® process is described below with respect to FIGS. 1A and 1B.
Referring to FIGS. 1A-1B, there are respectively illustrated a top view and side view of a 16×20 lens array 100 made from FOTOFORM® glass which was subjected to the SMILE® process. Basically, the SMILE® process subjects the FOTOFORM® glass to an ultraviolet light exposure step, a heat treatment step and if desired an ion exchange step to fabricate the traditional lens array 100. In particular, the traditional lens array 100 can be fabricated by exposing selected portions of the FOTOFORM® glass to ultraviolet light with wavelengths preferably between 240-400 nm (most preferable 300-350 nm) for approximately 3 minutes and then heat treating the exposed FOTOFORM® glass at 600° C. for 40 minutes. The traditional lens array 100 fabricated in this manner would have lenses 110 with a 5-15 μm sag height (see FIG. 1B). The traditional lens array 100 could also be subjected to an ion exchange treatment where the lens array 100 is immersed in a KNO3 salt bath at 500° C. for 64 hours. The ion exchange treatment causes the lenses 110 to take on an undesirable yellow color but also causes the sag heights of the lenses 110 to increase to approximately 38-61 μm (see TABLE 1). Sag is the parameter that controls the radius of curvature and, as such, the focal lengths and light gathering powers of the developed lenses 110 through the following expression:Rc=rL2/2δ  (1)where: Rc is the lens radius of curvature.                δ is the sag.        rL is the lens radius.        
Because, the color of the lenses 110 and the magnitude of the sag directly affects the performance of the lenses, scientists today are constantly trying to improve upon the composition of the photosensitive glass plate (FOTOFORM® glass) which is used to make a lens array. Accordingly, there is a need for a new composition of a photosensitive glass plate which can be used to make a lens array which has clear, colorless lenses exhibiting relatively large sag heights. This need and other needs are satisfied by the lens array and method of the present invention.